Central refrigeration system with automatic standby compressor capacity

ABSTRACT

A central refrigeration system for supermarkets and the like requiring two or more temperature levels of refrigerated fixtures wherein separate compressors operate the fixtures at different temperature levels and with only one or two large compressors for each temperature level. The system employs a single condenserreceiver for the refrigerant discharged from all of the compressors and a single oil separator for returning oil to the compressors. A control arrangement responsive to an abnormal increase in the suction pressure on a given compressor automatically operates a valving arrangement to transfer at least a portion of the refrigerant load on that compressor to another compressor normally operating fixtures at a different temperature level.

United States Patent [1113,580,006

[72] Inventor Lester K. Quick OTHER REFERENCES 868 wetview Crescent, Vancouver, British Jordan, R. c., and Priestea, B REFRIGERATION AND Columbus Canada AIR CONDITIONING. Englewood Cliffs, N.J., Prentice-Hall, m 2 3 0 Inc., 1956. p. 329- 344.

gg i g 1971 Primary ExaminerMartin P. Schwadron Assistant Examiner-P. D. Ferguson Attorney-Lyon & Lyon [54] CENTRAL REFRIGERATION SYSTEM WITH AUTOMATIC STANDBY COMPRESSOR ABSTRACT: A central refrigeration system for supermarkets CAPACITY and the like requiring two or more temperature levels of 1 Claims, 3 Drawing Figs. refrigerated fixtures wherein separate compressors operate the fixtures at different temperature levels and with only one [52] US. Cl 62/ 196, or two large compressors for each temperature leveL The 62/278 62/510 system employs a single condenser-receiver for the refrigerant [51] Int. Cl F 25b 5/00 discharged f all f the Compressors and a Single oil Separa [50] Field of Search 62/175, tor f returning oil to the compressors A control arrange 278 ment responsive to an abnormal increase in the suction pressure on a iven corn ressor automaticall o erates a valvin [56] References Cited arrangemeit to trans fer at least a portiozi o f the refrigeran t UNITED STATES PATENTS load on that compressor to another compressor normally 3,234,749 2/1966 Quick 62/510X operating fixtures at a different temperature level.

3/ 5/ A9 40 l I I I I t 59 5/ 3/ a/ 40 5 595, a@ l w 20 Va Patented May 25, 1971 3 Sheets-Sheet 1 INVENTOR 46576? ,6 dW/CL Arraeys Patented May 25, 1971 I5 Sheets-Sheet 2 INVENTOR (6576? 6 0/616 CENTRAL REFRIGERATION SYSTEM WITH AUTOMATIC STANDBY COWRESSOR CAPACITY This invention relates to central refrigeration systems used for operating refrigerated fixtures at various temperature levels and is particularly applicable to the refrigeration system of a supermarket wherein at least two distinct temperature levels are maintained in the refrigerated fixtures.

In recent years it has become more common and a recognized advantage to use large capacity compressors with appropriate condensers as a central refrigerant supply for a large number of refrigerated fixtures that may be located throughout a store or facility rather than individual compressors and condensers for each refrigerated fixture of perhaps for two or three identical fixtures. A number of advantages are achieved by using a central refrigeration system with large compressors such as permitting an efficient reclamation of the heat that is normally dissipated by the condensers to use such heat for heating the building, and providing a large quantity of compressed refrigerant available for use in defrosting selected refrigerated fixtures. However one of the recognized problems of using a single large compressor for all of the fixtures operated at a given temperature level is that if such compressor fails or malfunctions then the refrigeration of that entire group of fixtures is lost with the resultant loss of the refrigerated products. Even the use of a pair of relatively large compressors in parallel to operate all of the refrigerated fixtures at a given temperature level does not ensure that one compressor, upon the failure of the other, will be adequate to handle the refrigerant load of all of the fixtures during the time required for repairs or replacement except under certain circumstances and requirements. One such adequate capacity situation normally exists in the low-temperature requirements of a supermarket where one-half the normal compressor capacity would temporarily handle the low-temperature requirements.

The cost of large capacity compressors of the type used for central refrigeration systems for supermarkets and the like is so great as to economically prohibit the permanent installation of an extra compressor to function solely as a standby for the other compressors in the event of a failure of one of the other compressors. This is particularly true in view of the fact that while the threat of a compressor failure and loss of refrigerated product is very real the compressors are usually very dependable and the number of such failures is relatively small. Thus for a given supermarket installation an expensive standby compressor might never be used for an emergency standby.

Since many of the central refrigeration systems used in supermarkets and the like employ separate closed cycle systems for each of the different temperature levels, it is impossible to use the compressor of one system as a standby or a temporary replacement for the compressor of another system for many reasons such as; the difference in refrigerant used in the two systems, the fact that the properly operating system must then be disconnected, the difference in suction and discharge pressures in the two systems, the manual adjustments or changes to the substitute compressor that would be required, etc.

In summary, the principal object of this invention is to provide a central refrigeration system employing a single condenser-receiver arrangement for multiple temperature levels of fixtures wherein separate large compressors serve to operate the fixtures at each temperature level and a valving arrangement automatically serves to transfer at least a portion of the load from a malfunctioning or overload compressor operating fixtures of one temperature level to a compressor operating fixtures at a different temperature level whereby an automatic standby compressor capacity is achieved from the existing system compressors.

Another object of this invention is to provide a novel central refrigeration system employing multiple compressors operating fixtures at different temperature levels but using a common refrigerant charge wherein the compressing capacity of any one malfunctioning or nonoperating compressor is assumed by one or more of the other compressors for maintaining refrigeration of all of the fixtures during the required compressor replacement or repair.

A further object of this invention is to provide a central refrigeration system operating at least two different levels of refrigerated fixtures with at least two compressors operating the lower temperature fixtures wherein a valving arrangement serves to automatically shift at least part of the load from a malfunctioning compressor operating higher temperature fixtures to one of the two compressors for lower temperature fixtures. A still further object of this invention is to provide such a system wherein the load shift from the higher temperature compressor to the lower temperature compressor is in response to an abnormally high suction pressure on the higher temperature compressor which suction pressure is continuously monitored by a control arrangement for automatically causing the load shift.

Still another object of this invention is to provide a standby compressor capacity for central refrigeration systems employing multiple compressors with a single condenser-receiver arrangement regardless of whether all of the compressors are operating in parallel or compounded relationship, or whether only some of the compressors are compounded with others operating in parallel.

A further object of this invention is to provide a novel form of central refrigeration system wherein all of the fixtures of each temperature level requirement in the installation are operated by only one or two large compressors with all of the compressors employing a common oil separator and return system, a common refrigerant condenser and receiver arrangement, and a common hot gas defrosting system. A still further object of this invention is to provide such a central refrigeration system wherein at least part of the compressor capacity of each temperature level may be used as a standby for a malfunctioning or overloaded compressor operating the fixtures of a different temperature level.

Other and more detailed objects and advantages of the refrigeration system of this invention will appear from the following description and the accompanying drawings wherein:

FIG. I is a diagrammatic illustration of one form of the refrigeration system of this invention wherein all of the compressors for operating the various temperature level fixtures are in parallel relationship.

FIG. 2 is a diagrammatic illustration of another form of the refrigeration system of this invention wherein separate compressors operate three different temperature levels of fixtures which normally are in compounded relationship and a separate air conditioning compressor is incorporated in the system and usable for standby compressor capacity.

FIG. 3 is a diagrammatic illustration of still another form of the refrigeration system of this invention similar to that of FIG. 2 but wherein only the compressor operating the lowest temperature level fixtures is in compounded relationship with respect to the other compressors.

For convenience and clarity of description, the refrigeration systems of this invention will be described in relation to an installation in asupermarket, since presently that is the most common use for such a system, but it will readily be understood by those skilled in the art that the refrigeration system of this invention is equally applicable to any type of installation having similar refrigeration requirements. Further while each of the three refrigeration systems illustrated in the drawings will be described as having a specific number of compressors installed in a specific manner it is to be understood and will be readily appreciated by those skilled in the art that more or fewer compressors might be used in any specific installation as determined by the particular requirements of that installation without departing from this inventron.

Referring now more particularly to FIG. I of the drawings, the refrigeration system is illustrated as employing three compressors l0, l1 and 12 which may be of different types and capacities depending on the requirements of the installation,

although normally compressors 10 and 11 will be of the same since they are operating in parallel on the same refrigerant load, as hereinafter appears more fully. The compressors 10, 11 and 12 are in parallel relationship and the discharge from each compressor is connected to an oil separator device 13 either directly from each compressor or through a common header 14 as shown in the drawings. The oil separator device 13 serves to separate and retain the oil entrained with the compressed refrigerant discharged from the compressors. The compressed refrigerant passes out of device 13 through conduit 15 to the system condenser 16 wherein the entire compressed refrigerant output of the compressors 10, 11 and 12 is condensed. From the condenser 16 the liquid refrigerant passes through a conduit 17 to a liquid refrigerant header 18 and a supply of the liquid refrigerant is retained in receiver 19 which is here illustrated as a surge-type receiver. An equalizing line 20 connects the inlet side of the condenser 16 with the top of the receiver 19.

The common supply of liquid refrigerant from condenser 16 and receiver 19 is connected through liquid header 18 to the evaporators of all of the refrigerated fixtures of the installation. For convenience of illustration the refrigerated fixtures have not been shown and only the evaporators and the associated valving controls have been diagrammatically illus trated in this FIG. as well as FIGS. 2 and 3. The system illustrated in FIG. 1 is adapted to operate refrigerated fixtures of two different temperature levels which in supennarket installations are commonly referred to as the low temperature fixtures and the standard temperature fixtures. The specific temperature of each fixture will vary within a limited range but in a given installation a desired suction temperature will be selected for each of the two temperature fixtures and +l0 F. for the standard temperature fixtures. In the system of FIG. 1 evaporators 21, 22, 23, 24 and 25 are illustrated as the lowtemperature evaporators and evaporators 26, 27, 28, 29 and 30 are illustrated as the high or standard temperature evaporators. While 10 evaporators have been shown with one-half as low temperature and one-half as standard temperature it will be appreciated by those skilled in the art that any number of evaporators may be used and the number of low-temperature evaporators need not be related to the number of high-temperature evaporators. Each of the evaporators 21 through 30 are identical and relatively conventional in their refrigeration operation and control although in the defrosting arrangement evaporators 29 and 30 differ from the remaining evaporators. Each of the evaporators is connected to the liquid refrigerant header 18 witheach evaporator having a conventional expansion valve 31 on the inlet of the evaporator and controlled in response to the outlet temperature of the evaporator by means of the sensing bulb 32. A temperature-sensitive modulating valve 33 is provided on the outlet of each evaporator for controlling the back pressure on the evaporator and such valve may be of any conventional type such as that shown in my U.S. Pat. No. 3,316,731. The valve 33 has a sensing bulb 34 responsive to the fixture temperature for controlling the opening and closing of the valve in response to a variation from the preselected desired temperature of the fixture.

Although it forms no part of the present invention other than illustrating the versatility of the system, evaporators 21 through 28 are shown with appropriate valving for causing hot gas defrosting of each of such evaporators. Evaporators 29 and 30 are not valved for hot gas defrosting and would be of the type that employs either off-cycle defrosting or perhaps electric heating for defrosting. Downstream of the modulating valve 33, the outlet of each evaporator 21 through 28 is provided with a three-way valve 35 for selectively connecting the outlet of each evaporator to either a hot gas header 36 or the respective suction headers connected to the compressors. The valve 35 associated with evaporator 28 is illustrated in the position connecting the evaporator to the hot gas header 36 for supplying gaseous refrigerant to the evaporator for defrosting. As disclosed in my U.S. Pat. No. 3,343,375 the gaseous refrigerant for defrosting need not be at a highly elevated temperature and therefore it is preferred that such gaseous refrigerant be taken, for example, from the top of the receiver 19 rather than directly from the compressors. The gaseous refrigerant passes freely in a reverse direction through modulating valve 33 into the evaporator 28 and then out through bypass conduit 37 to a condensate header 38. Each bypass conduit 37 is provided with a normally closed solenoid valve 39 which is opened upon movement of valve 35 to the position to admit gaseous defrosting refrigerant to the associated evaporator. Further, each bypass conduit 37 may be provided with a check valve 40 to prevent reverse flow from the condensate header 38 into an evaporator as may otherwise occur due to the particular construction of the solenoid valve 39. The defrosting refrigerant passes from header 38 through conduit 41 to an accumulator 42 from which the gaseous refrigerant returns through conduit 43 to the suction of compressor 12 and any liquid refrigerant is slowly bled through conduit 44 into the suction of compressor 12. This defrosting system is broadly similar to that which is more fully described in my U.S. Pat. No. 3,234,752.

The outlets of the low-temperature evaporators 21 through 25 are connected through the valves 35 to a low-temperature suction header 45. Similarly the outlets of the standard temperature evaporators 26 through 30 are connected to a separate, standard temperature suction header 46. The lowtemperature suction header 45 is connected through a conduit 47 to both an intermediate header 48 and the suction side of compressor 10. Similarly the standard temperature suction header 46 is connected through a conduit 49 to both the inter mediate header 48 and the suction accumulator 42 and in turn through conduit 43 to the suction of compressor 12. A conduit 50 connects the suction side of compressor 11 to a point 51 in the intermediate header 48. A check valve 52 is provided in header 48 between the low-temperature suction conduit 47 and the point 51 which serves to prevent the flow of refrigerant in the direction from point 51 toward suction conduit 47 while freely allowing flow in the reverse direction. A modulating valve 53 is positioned in the intermediate suction header 48 between the point 51 and the standard temperature suction conduit 49. Valve 10 modulates between the opened and closed position in response to the hereafter described controls and conditions and therefore it may be seen that the suction of compressor 11 is normally connected to the low-temperature side of the system but upon opening of valve 53 will be connected to the standard temperature side of the system.

As shown in FIG. 1 the valve 53 is of the pilot-operated type normally referred to as either a suction pressure control valve or an evaporator pressure regulator valve although it will readily appear to those skilled in the art that a variety of other types of valves might be used to accomplish the hereinafter described functions of valve 53 with or without the same or similar controls. The pilot portion 54 of valve 53 is connected by a small supply conduit 55 to both the low-temperature suction conduit 47 and the standard temperature suction 49, effectively in parallel relation with the intermediate suction header 48. A capillary tube 56 or any other convenient form of flow restrictor is connected in line 55 between low-temperature suction conduit 47 and the pilot portion 54 of the valve. A small, normally closed solenoid valve 57 is connected in line 55 between the standard temperature suction conduit 49 and the pilot portion 54. By this arrangement the pilot section 54 of the modulating valve may be exposed to two vastly different pressure levels depending on the opening or closing of the valve 57 and even the resultant pressure when valve 57 is open will depend on the relative pressures in the conduits 47 and 49.

Under normal operating conditions valve 57 is closed whereby the pilot section 54 of the modulating valve 53 is exposed to the low pressure of the low-temperature suction side of the system and valve 53 will be modulated to a tightly closed position. Solenoid valve 57 is operated by a pressure control 58 which is in turn responsive to the pressure in the standard temperature suction header 46. When the pressure in suction header 46 exceeds a predetermined level thereby indicating that standard temperature compressor 12 is malfunctioning or overloaded, pressure control 58 actuates the solenoid valve 57 to an open position to impose the high pressure in conduit 49 on the pilot portion 54 of the modulating valve thereby causing opening of valve 53. A portion of this imposed pressure will be continually bled off through capillary tube 56 to the low-temperature conduit 47 with the resultant pressure on the pilot portion 54 determining the modulated position of valve 53. The opening of valve 53 permits the compressor 11 to assume part if not all of the standard temperature suction load from header 46. If the malfunctioning or overload of compressor 12 is only temporary whereby the pressure in standard temperature suction header 46 is soon reduced to the acceptable level, then pressure control 58 responds to such reduction and closes valve 57 whereby the pressure on pilot section 54 diminishes and valve 53 modulates to a closed position thereby automatically returning compressor 11 to the low-temperature side of the system.

If the abnormal pressure level in suction header 46 is a result of a complete failure of standard temperature compressor 12 then modulating valve 53 will remain open until the necessary repairs are made and compressor 1] assumes the entire standard temperature load including the reevaporation of condensed refrigeration returned to accumulator 42 during defrosting although emergency controls may be provided for suspending further defrost cycles until repair of compressor 12. Under such circumstances the pressure in header 46 and in turn at point 51 of intermediate header 48 will be substantially higher than the pressure in low-temperature suction 4 header 45 and therefore the check valve 52 will be completely closed whereby compressor handles the entire low-temperature refrigeration load and compressor 11 handles the entire standard temperature refrigeration. load.

However if the abnormally high pressure in standard temperature suction header 46 is merely the result of an abnormally high refrigeration load, such as during initial pull down or after the defrost of a large fixture, then compressor 11 will serve merely to assist compressor 12 during the continuance of this abnormal refrigeration load. Under such circumstances valve 53 would be modulated to a partially open position to effectively transfer only a portion of the excessive standard temperature refrigeration load and the pressure in intermediate header 48 at point 51 would be at someintennediate level. The pressure at point 51 may even be sufficiently low for check valve 52 to remain partially open whereby compressor 11 continues to assume a portion of the low-temperature refrigeration load. For example with refrigerant R-502 the typical desired suction pressure on header 46 might be 4l pounds and on low-temperature suction header 45 it might be 4.3 pounds. However with compressor 11 assuming some of such abnormal standard temperature load thereby shifting the low-temperature load to compressor 10, the pressure in the low-temperature suction header 45 would be expected to increase to perhaps 16 pounds and yet with valve 53 only partially open the pressure in intermediate suction header 48 at point 51 might be only 7 or 8 pounds whereby check valve 52 would partially open to allow compressor 11 to simultaneously function as both a low-temperature and standard temperature compressor. Thus a completely automatic standby for compressor 12 is achieved for both malfunctioning of the compressor 12 and mere temporary overload conditions.

The refrigeration system of FIG. 1 is also provided with an arrangement for compressor 12 to act as a standby for the lowtemperature compressors 10 and 11 if both such compressors were to fail at the same time which would be extremely rare. This standby is affected by the closing of valve 59 to relieve compressor 12 from the entire standard temperature refrigeration load and the opening of modulating valve 53 to connect the suction of compressor 12 to the low-temperature suction header 45. Of course under such circumstances the standard temperature fixtures are no longer refrigerated but the products contained in such fixtures will not spoil as rapidly as those contained in the low-temperature fixtures without refrigeration.

In addition an alarm system may be provided with the refrigeration systems of this invention and, as shown in FIG. 1, may include a time delay clock 60 actuated by pressure control 58 upon the occurrence of an abnormally high pressure in standard temperature suction header 46. After a predetermined time period longer than norrnally would be encountered upon a mere abnormal refrigeration load in the standard temperature fixtures, the clock 60 will sound an alarm thereby indicating a probable malfunction of compressor 12. Similarly a pressure control 61 and time delay alarm 62 may be provided on the low-temperature suction conduit 47 to indicate an abnormally high suction pressure continuing over an extended period of time.

The refrigeration system of FIG. 1 is also illustrated with an oil return arrangement essential to a system having multiple compressors and a single condenser-receiver. Each of the compressors 10, 11 and 12 is provided with a float valve 63 responsive to the oil level in the respective compressor and an oil return line 64 is connected from the oil separator device 13 to the fioat valves 63. The oil separator device 13 also serves as a reservoir for a supply of oil and thus the oil level in each of the compressors is continuously maintained at the proper level.

Referring now to FIG. 2, .a refrigeration system employing this invention is diagrammatically illustrated and, in addition to the previously described compressors, incorporates the compressor for the building air conditioning system and a separate compressor for extremely low-temperature fixtures. A group of evaporators for standard temperature fixtures are illustrated as evaporators 101, 102 and 103, similar to evaporators 26 through 30 of FIG. 1. The low-temperature evaporators are illustrated as 104, 105 and 106, similar to evaporators 21 through 25 of FIG. 1. In addition an extremely low-temperature evaporator 107 is illustrated and in a supermarket installation this evaporator might be associated with an ice cream freezer or other refrigerated fixture requiring extremely low temperature. Thus the suction temperature on evaporator 107 might be approximately -50 F. while, as previously described, the suction temperatures on the lowtemperature evaporators 104, 105 and 106 might be 25 F. and on evaporators 101, 102 and 103 it might be +l0 F. Again each evaporator is provided with the conventional refrigeration and temperature controls such as expansion valve 108 with sensing bulb 109 and back pressure modulating valve 110 with temperature-sensing bulb 111. Evaporators 101-107 are arranged for' hot gas defrosting but the system employed is somewhat different from that which has been shown and described in FIG. 1. For purposes of illustrating that the refrigeration system of this invention does not dictate or limit the type of hot gas defrosting system that may be used. In the system of FIG. 2 a hot gas header 112 is connected from the top of the refrigerant-receiver 113 through a three-way valve 114 associated with each evaporator for supplying saturated gaseous refrigerant to the evaporator to be defrosted and specifically valve 114 associated with evaporator 103 is illustrated in the open position for defrosting evaporator 103. A branch conduit 115 connects each evaporator to a header 116 and a normally closed solenoid valve 117 controls the flow through the branch conduit to the header. This defrosting arrangement is similar to the arrangement described more fully in my U.S. Pat. No. 3,234,753. The defrosting system of FIG. 2 operates by opening the valve 117 associated with the evaporator being defrosted whereby the defrosting refrigerant flows into the header 116 and then in a reverse direction through any one of the solenoid valves 117, since the construction of the valves 117 do not prevent such reverse flow, to thereby dispose of the defrosting refrigerant. To ensure that at least one evaporator will be in a condition to accept and dispose of defrosting refrigerant, a control 188 responsive to excessive pressure in header 116 serves to close one or more of the expansion valves 108 thereby discontinuing the normal supply of refrigerant to that evaporator whereby refrigerant will flow from header 116 into that evaporator until the pressure in header 116 is reduced.

In the refrigeration system of FIG. 2 there are six compressors illustrated and for convenience such compressors will be referred to by their normal relationship to the evaporators operated by each compressor although it will readily be understood that during standby operation or overload conditions one or more of the compressors will operate different evaporators as hereinafter described. The ultralow temperature compressor 120 has its suction connected through conduit 121 to the ultralow temperature evaporator 107. A pair of low-temperature compressors 122 and 123 have their suctions connected through a low-temperature suction header 124 to the low-temperature evaporators 104, 105 and 106. A pair of standard temperature compressors 125 and 126 have their suctions connected to a standard temperature suction header 127. An air conditioning compressor 128 normally has its suction connected through conduit 129 to an air conditioning evaporator 130 which is in turn connected through a conduit 131 to the liquid refrigerant header 132 that extends from the receiver 113 to all of the evaporators. Before reaching the receiver 113 all of the compressed refrigerant from compressors 120, 122, 123, 125, 126 and 128 passes through the oil separator device 133 (which functions the same as oil separator device 113 described with respect to FIG. 1) and then through conduit 134 and condenser 135 to the receiver 113. The discharge of ultralow temperature compressor 120 is connected through conduit 136 to the low-temperature suction header 124 thereby compounding the load of compressor 120 with the low-temperature load to compressors 122 and 123 and as a result the compression ratio on ultralow temperature compressor 120 is always at a very acceptable level. Lowtemperature compressors 122 and 123 normally operate in parallel relationship and have their discharge conduits 137 and 138, respectively, connected through a header 139 to the suctions of standard temperature compressors 125 and 126 thereby compounding the low-temperature loads, including the ultralow temperature load, with the standard temperature loads on compressors 125 and 126. The discharge conduits 140 and 141 from compressors 125 and 126, respectively, are connected to the oil separator device 133 as is the discharge conduit 142 of air conditioning compressor 128 to thereby complete the normal refrigeration cycle. Some of the advantages of compounding refrigerant loads of different temperature levels are set forth in my US. Pat. No. 3,234,749.

Under normal loads and compressor-operating conditions, the compressors of the refrigeration system of FIG. 2 will operate in the aforedescribed manner. If there is a malfunctioning or overloading of ultralow temperature compressor 120 whereby the pressure in discharge conduit 136 drops below that which is being maintained in low-temperature suction header 121, a check valve 143 in bypass conduit 144 will open to allow refrigerant to pass from suction conduit 121 to suction header 124 without passing through compressor 120. This serves to automatically maintain a suction on ultralow temperature evaporator 107 although such suction will be substantially higher pressure than the desired suction pressure on that evaporator but under normal conditions will be adequate to preserve the product contained in that fixture until the malfunction is corrected or the overload diminishes.

In the event of an overload in the standard temperature load or a malfunctioning of compressor 125 of compressor 126 in the system of FIG. 2, the pressure in standard temperature suction header 127 will reflect such condition by increasing to an abnormal level. A pressure control device 145 senses the pressure in suction header 127 and upon reaching a given abnormal pressure will actuate a solenoid valve 146 in discharge conduit 37 of low-temperature compressor 122 to close valve 146 whereby the discharge of compressor 122 will be diverted through conduit 147 directly to the oil separator device 133. Of course since the pressure in oil separator 133 is substantially higher than the normal discharge pressure from compressor 122, the conduit 147 is provided with a check valve 148 to prevent reverse flow under normal operation and once the discharge pressure of compressor 122 has increased to the same level as the discharge pressures of compressors and 126 the check valve 148 will open to pass the compressed refrigerant into the oil separator device 133. In this manner the refrigerant load of compressor 122 which is normally added to the suction load of compressors 125 and 126 is removed from compressors 125 and 126 thereby tending to reduce the pressure sensed by control device 145. If the condition giving rise to actuation of device and closing of valve 146 is merely a temporary overload than this reduction in load normally will suffice until the pressure again drops to the acceptable level whereby valve 146 will be opened to return the system to the normal compounded arrangement. If the abnormal pressure condition continues or increases in suction header 127 control 145 will serve to close valve 149 in discharge conduit 138 to divert the discharge of compressor 123 to conduit 150 and into oil separator device 133 to further reduce the load on standard temperature compressors 125 and 126. Conduit 150 is also provided with a check valve 151 identical to the aforedescribed check valve 148.

In addition to the aforedescribed standby compressor capacity within the regular refrigeration system of FIG. 2, the air conditioning compressor 128 may be also used as a standby or supplement for any of the other compressors and this may be either a manual operation or the automatic arrangement shown. The low-temperature suction header 124 is connected through a solenoid valve 152 to the suction conduit 129 of air conditioning compressor 128 and valve 152 is operated in response to pressure control 153. When the suction pressure in low-temperature suction header 124 exceeds a predetermined value indicated an overload or compressor malfunction the control 153 opens valve 152 and closes valve 154 on the inlet of the air conditioning evaporator 130 whereby the air conditioning compressor 128 will be connected in parallel with the low-temperature compressors 122 and 123. Compressor 128 may also be connected in parallel to standard temperature compressors 125 and 126 by opening the valve 155 between low temperature discharge header 139 and compressor suction header 129 and this operation may be controlled by the same pressure control 145 responsive to suction pressure in the standard temperature suction header 127. The control 145 may be set to actuate the valves 146, 149 and 155 in any desired sequence in response to different levels of excessive pressure. Suitable alarms similar to alarms 60 and 62 described with respect to FIG. 1 may also be provided.

Referring now to the refrigeration system of FIG. 3, many of the components are identical to those described with respect to FIG. 2 and will be numbered in the 200 series corresponding to the 100 series numeral of the same component in FIG. 2. Again three standard temperature evaporators 201, 202 and 203, three low-temperature evaporators 204, 205 and 206 and an ultralow temperature evaporator 207 are shown for illustrating the refrigeration system of this invention. Similarly expansion valves 208, back pressure modulating valves 210, three-way defrost control valves 214 and bypass conduit valves 217 are provided and have the same functions previously described for valves, 108, 110, 114 and 117, respectively. A liquid refrigeration header 232 connects the bottom of the receiver to each of the evaporators for supplying liquid refrigerant and a hot gas header 212 connects the top of the receiver to the evaporators through the valves 214 for defrosting purposes. A condensate header 216 connects all of the evaporators for distributing the condensed defrosting refrigerant and may be provided with a control 218 as aforedescribed. The ultralow temperature compressor 220 has a suction conduit 221 connected to the ultralow temperature evaporator 207 and similar low-temperature and standard temperature suction headers 224 and 227, respectively, are provided. The discharge 0 iltralow temperature compressors 220 is again connected t trough conduit 236 to the suction header 224 and a bypass conduit 244 with a check valve 243 is also provided. One low-temperature compressor 222 is connected directly to the suction header 224 while the other lowtemperature compressor 223 is separated from the header by a check valve 260 which under normal operating conditions is open to allow the free passage of refrigerant from header 224 to compressor 223. The discharge conduits 237 and 238 connect the low-temperature compressors 222 and 223, respectively, directly to the oil separator device 233. Standard temperature compressors 225 and 226 have their suctions connected directly to standard temperature suction header 227 and have their discharges connected by conduits 240 and 241, respectively, to the oil separator device 233. In turn the oil separator device 233 is connected by conduit 234 to condenser 235 and then to the receiver 213 to complete the refrigeration cycle. Thus under normal operating conditions the ultralow temperature compressor 220 is compounded to the two parallel low-temperature compressors 222 and 223 which operate in parallel with the two standard temperature compressors 225 and 226. Since the discharge pressures of compressors 222, 223, 225 and 226 are the same, the compression ratio of compressors 222 and 223 is greater than that of compressors 225 and 226.

in the refrigeration system of FIG. 3 the standard temperature suction header 227 is connected by a conduit 26] through a solenoid valve 262 and conduit 263 to the suction side of low-temperature compressor 223. The solenoid valve 262 is operated by pressure control 245 responsive to abnormally high pressures in the suction header 227. When a compressor malfunction or an overload in the standard temperature fixtures occurs the increased pressure is sensed by the control 245 which functions to open the normally closed valve 262 thereby connecting the suction of low-temperature compressor 223 to the standard temperature load in parallel with compressors 225 and 226. The higher suction pressure causes the check valve 260 to close wherebylow-temperature compressor 222 handles the entire low-temperature load from suction header 224 and, in essence, compressor 223 automatically becomes a standard temperature compressor. As the pressure in suction header 227 declines to the normal level due to a termination of the overload or correction of the malfunction, the control 245 closes valve 262 to automatically place the low-temperature compressor 223 back onto the lowtemperature load. Normally the single low-temperature compressor 222 will be of adequate capacity to maintain operation of the low-temperature evaporators while compressor 223 is assisting with the standard temperature load. Moreover the air conditioning compressor 228 may be used as a standby similar to the arrangement in FIG. 2 by opening valve 252 to connect the compressor to the low-temperature suction or by opening valve 255 to connect the compressor to the standard tempera ture suction.

Thus it may be seen that by this invention there is provided a central refrigeration system employing multiple compressors functioning to operate refrigerated fixtures at distinctly different temperature levels with but a single condenser-receiver arrangement and whereby standby compressor capacity is available during times of malfunctions or overload without the necessity of providing a separate, otherwise unused, compressor. Moreover by the three systems herein disclosed it is clearly illustrated that this invention is not limited to solely parallel or compounded compressor arrangements. This invention is not limited to the three herein disclosed refrigeration systems or the detail thereof but rather is of the full scope of the appended claims.

lclaim:

1. In a central refrigeration system for operating a plurality of refrigerated fixture evaporators at two or more different temperature levels, the combination of, at least three separate compressors for operating the fixtures, at least one said compressor having its suction nonnally connected to the fixture evaporators operating at a given temperature level, a single condenser-receiver means for receiving and condensing the compressed refrigerant output of all of said compressors and connected to all of the fixtures for supplying refrigerant to the fixture evaporators, and controlled valve means responsive to an abnormal increase in the load on one of said compressors for automatically transferring at least a portion of the refrigerant load on that one compressor to another said compressor normally operating only fixture evaporators at a different temperature level than the said one compressor for functioning as an automatic standby compressor for said one compressor.

2. The refrigeration system of claim 1 wherein a third compressor operates the same refrigerated fixture evaporators in parallel with the said compressor functioning as a standby compressor for assuming at least a portion of the normal load of said standby compressor during such standby operation.

3. The refrigeration system of claim 2 wherein said third compressor and said standby compressor normally operate the refrigerate fixtures of a lower temperature level than those operated by said one compressor.

4. The refrigeration system of claim 1 wherein said con-v trolled valve means includes a control means responsive to an abnormally high suction pressure on said one compressor for actuating said controlled valve means to effect said load transfer.

5. The refrigeration system of claim 1 wherein there are two temperature levels and said controlled valve means includes an intermediate suction header connecting the suctions of all the refrigerated fixture evaporators and a valve in said header between respective compressors and the fixture evaporator for said load transferring.

6. The refrigeration system of claim 5 wherein said valve has modulating means for variably controlling such communication, and means are provided for actuating said modulating means in response to the degree of overload on said one compressor.

7. The refrigeration system of claim 6 wherein said valve has pilot-operated section for modulating and said actuating means includes a conduit connecting said section to the suctions of both levels of fixture evaporators, and said conduit is provided with a flow-restricting portion between said pilotoperated section and the lower temperature level suction and another valve between said section and the higher temperature level suction, said latter valve operated in response to the overload condition.

8. The refrigeration system of claim 5 wherein a third compressor operates the same refrigerated fixtures in parallel with said standby compressor, said standby compressor is connected to said intermediate header in a downstream direction from the connection to said third compressor, and a check valve is provided in that portion of said intermediate header between the connections of said third and standby compressors for isolating said third compressor from the overload on the one compressor.

9. The refrigeration system of claim 1 wherein a space air conditioning system is provided and comprises another separate compressor and an air conditioning evaporator, said separate compressor having its suction connected to said air conditioning evaporator and its discharge connected to said single condenser-receiver means in parallel with the other compressors.

10. The refrigeration system of claim 9 wherein valve means are provided for selectively connecting the suction of said separate compressor to said selected refrigerated fixture evaporators upon the occurrence of an excess suction pressure on said selected refrigerated fixtures.

11. The refrigeration system of claim 1 wherein a third compressor is provided and operates the same refrigerated fixtures in parallel with said standby compressor and both said third and standby compressors operating in parallel with said one compressor, and said valve-controlled means includes a conduit connecting the suction of said one compressor to the suction of the standby compressor with a normally closed valve in said conduit operated to an open position by an excess pressure on the suction of said one compressor. I

12. The refrigeration system of claim 11 wherein a conduit connects the suctions of said third and standby compressors and a check valve is provided in said conduit to prevent flow from the suction side of said one compressor to the suction side of said third compressor.

13. The refrigeration system of claim 1 wherein a third compressor is provided and operates the same refrigerated fixtures in parallel with said standby compressor, said third and stand by compressors having a header connecting their discharge sides normally connected to the suction side of said one compressor in compounded relationship, a bypass conduit means connecting the discharge sides of said third and standby compressors to said single condenser-receiver means, and said controlled valve means including normally open valve means in said header operated to a closed position upon said overload of the one compressor to direct the discharge of said third and standby compressors through said bypass conduit means.

14. The refrigeration system of claim 13 wherein a separate said normally open valve means is provided with each compressor, and control means sequentially actuate said valve means in response to different magnitudes of overload.

15. The refrigeration system of claim 13 wherein a check valve means is provided in said bypass conduit means for preventing reverse refrigerant flow toward the discharge sides of said third and standby compressors.

16. In a central refrigeration system for operating a plurality of refrigerated fixture evaporators at two or more different temperature levels, the combination of, at least three separate compressors for operating the fixtures, at least one said compressor having its suction nonnally connected to the fixture evaporators operating at a given temperature level, a single condenser-receiver means for receiving and condensing the compressed refrigerant output of all of said compressors and connected to all of the fixtures for supply refrigerant to the fixture evaporators, a single oil separator-receiver means connected between said compressors and the condenser-receiver means for separating oil from the refrigerant and having means for returning the oil to each of said compressors, valve means on the suction side of the fixture evaporators for modulating and controlling the pressure in each evaporator in relation to the desired temperature level substantially uneffected by any lower compressor suction pressure, and control means responsive to an abnormal increase in the suction pressure to one of said compressors with said control means including valve means for automatically discontinuing at least a portion of the refrigerant load to that one compressor and imposing that said refrigerant load on another said compressor that normally operates fixture evaporators at a different temperature level than the said one compressor for serving as an automatic standby for said one compressor.

17. The refrigeration system of claim 16 wherein a space air conditioning system is provided and comprises another separate compressor and an air conditioning evaporator, said separate compressor having its suction connected to said air conditioning evaporator and its discharge connected to said single condenser-receiver means in parallel with the other compressors.

18. The refrigeration system of claim 17 wherein valve means are provided for selectively connecting the suction of said separate compressor to selected refrigerated fixture evaporators upon the occurrence of an excess suction pressure on said selected refrigerated fixtures. 

1. In a central refrigeration system for operating a plurality of refrigerated fixture evaporators at two or more different temperature levels, the combination of, at least three separate compressors for operating the fixtures, at least one said compressor having its suction normally connected to the fixture evaporators operating at a given temperature level, a single condenser-receiver means for receiving and condensing the compressed refrigerant output of all of said compressors and connected to all of the fixtures for supplying refrigerant To the fixture evaporators, and controlled valve means responsive to an abnormal increase in the load on one of said compressors for automatically transferring at least a portion of the refrigerant load on that one compressor to another said compressor normally operating only fixture evaporators at a different temperature level than the said one compressor for functioning as an automatic standby compressor for said one compressor.
 2. The refrigeration system of claim 1 wherein a third compressor operates the same refrigerated fixture evaporators in parallel with the said compressor functioning as a standby compressor for assuming at least a portion of the normal load of said standby compressor during such standby operation.
 3. The refrigeration system of claim 2 wherein said third compressor and said standby compressor normally operate the refrigerate fixtures of a lower temperature level than those operated by said one compressor.
 4. The refrigeration system of claim 1 wherein said controlled valve means includes a control means responsive to an abnormally high suction pressure on said one compressor for actuating said controlled valve means to effect said load transfer.
 5. The refrigeration system of claim 1 wherein there are two temperature levels and said controlled valve means includes an intermediate suction header connecting the suctions of all the refrigerated fixture evaporators and a valve in said header between respective compressors and the fixture evaporator for said load transferring.
 6. The refrigeration system of claim 5 wherein said valve has modulating means for variably controlling such communication, and means are provided for actuating said modulating means in response to the degree of overload on said one compressor.
 7. The refrigeration system of claim 6 wherein said valve has pilot-operated section for modulating and said actuating means includes a conduit connecting said section to the suctions of both levels of fixture evaporators, and said conduit is provided with a flow-restricting portion between said pilot-operated section and the lower temperature level suction and another valve between said section and the higher temperature level suction, said latter valve operated in response to the overload condition.
 8. The refrigeration system of claim 5 wherein a third compressor operates the same refrigerated fixtures in parallel with said standby compressor, said standby compressor is connected to said intermediate header in a downstream direction from the connection to said third compressor, and a check valve is provided in that portion of said intermediate header between the connections of said third and standby compressors for isolating said third compressor from the overload on the one compressor.
 9. The refrigeration system of claim 1 wherein a space air conditioning system is provided and comprises another separate compressor and an air conditioning evaporator, said separate compressor having its suction connected to said air conditioning evaporator and its discharge connected to said single condenser-receiver means in parallel with the other compressors.
 10. The refrigeration system of claim 9 wherein valve means are provided for selectively connecting the suction of said separate compressor to said selected refrigerated fixture evaporators upon the occurrence of an excess suction pressure on said selected refrigerated fixtures.
 11. The refrigeration system of claim 1 wherein a third compressor is provided and operates the same refrigerated fixtures in parallel with said standby compressor and both said third and standby compressors operating in parallel with said one compressor, and said valve-controlled means includes a conduit connecting the suction of said one compressor to the suction of the standby compressor with a normally closed valve in said conduit operated to an open position by an excess pressure on the suction of said one compressor.
 12. The refrigeration system of claim 11 wherein a conduit Connects the suctions of said third and standby compressors and a check valve is provided in said conduit to prevent flow from the suction side of said one compressor to the suction side of said third compressor.
 13. The refrigeration system of claim 1 wherein a third compressor is provided and operates the same refrigerated fixtures in parallel with said standby compressor, said third and standby compressors having a header connecting their discharge sides normally connected to the suction side of said one compressor in compounded relationship, a bypass conduit means connecting the discharge sides of said third and standby compressors to said single condenser-receiver means, and said controlled valve means including normally open valve means in said header operated to a closed position upon said overload of the one compressor to direct the discharge of said third and standby compressors through said bypass conduit means.
 14. The refrigeration system of claim 13 wherein a separate said normally open valve means is provided with each compressor, and control means sequentially actuate said valve means in response to different magnitudes of overload.
 15. The refrigeration system of claim 13 wherein a check valve means is provided in said bypass conduit means for preventing reverse refrigerant flow toward the discharge sides of said third and standby compressors.
 16. In a central refrigeration system for operating a plurality of refrigerated fixture evaporators at two or more different temperature levels, the combination of, at least three separate compressors for operating the fixtures, at least one said compressor having its suction normally connected to the fixture evaporators operating at a given temperature level, a single condenser-receiver means for receiving and condensing the compressed refrigerant output of all of said compressors and connected to all of the fixtures for supply refrigerant to the fixture evaporators, a single oil separator-receiver means connected between said compressors and the condenser-receiver means for separating oil from the refrigerant and having means for returning the oil to each of said compressors, valve means on the suction side of the fixture evaporators for modulating and controlling the pressure in each evaporator in relation to the desired temperature level substantially uneffected by any lower compressor suction pressure, and control means responsive to an abnormal increase in the suction pressure to one of said compressors with said control means including valve means for automatically discontinuing at least a portion of the refrigerant load to that one compressor and imposing that said refrigerant load on another said compressor that normally operates fixture evaporators at a different temperature level than the said one compressor for serving as an automatic standby for said one compressor.
 17. The refrigeration system of claim 16 wherein a space air conditioning system is provided and comprises another separate compressor and an air conditioning evaporator, said separate compressor having its suction connected to said air conditioning evaporator and its discharge connected to said single condenser-receiver means in parallel with the other compressors.
 18. The refrigeration system of claim 17 wherein valve means are provided for selectively connecting the suction of said separate compressor to selected refrigerated fixture evaporators upon the occurrence of an excess suction pressure on said selected refrigerated fixtures. 